The present invention relates to a device for absorbing impulsive torques applied to a motor combined with a worm gear, such for example as a motor for use in an automobile window regulator.
There are known worm gears meshing with worms on the output shafts of motors. Since the output shaft of the motor is locked against rotation when the worm gear is forcibly rotated and the worm and worm gear coupling provides a large speed reduction ratio, the motor coupled with the worm gear finds many applications in which the object driven by the motor is to be held in a stopped position and the motor is subjected to a low-speed, high-torque load. The self-locking capability of the worm and worm gear mechanism is however disadvantageous in that the teeth of the worm and worm gear may be broken when an undue impulsive torque is imposed thereon in a reverse direction because the impact force is directly applied to the teeth inasmuch as the motor output shaft is not rotated by the worm gear.
In uses where the motor is to be started and stopped repeatedly, impulsive torques are generated due to the moment of inertia of the motor and the load to apply impact forces to the teeth of the worm and worm gear.
The foregoing problems are experienced particularly with drive motors for use in window regulators and sliding roof mechanisms in automobiles.
One known motor with a worm gear, incorporating a conventional device for absorbing impulsive torques, is illustrated in FIGS. 1 through 6. As shown in FIGS. 1 and 2, the rotative power from a motor output shaft 1 is transmitted to a worm gear or wheel 2 and then to a power output shaft 7 through a device for absorbing impulsive torques. As illustrated in FIGS. 3 and 4, the known device for absorbing impulsive torques is composed of an annular damper 5 of rubber which is bonded in joined relation to an inner ring 6 of iron and an outer ring 4 of iron. The joined assembly of the annular damper 5 and the inner and outer rings 6, 4 is force-fitted in an iron ring 3 having a plurality of tongues 3a fitted respectively in slots 2a defined in the worm gear 2, also as shown in FIGS. 5 and 6.
FIGS. 7 and 8 illustrate another conventional device for absorbing impulsive torques. This device has no outer ring, but the annular damper 5 is positioned between the inner ring 6 and a ring 3a' with its tongues 3 fitted in the slots in the worm gear.
The illustrated prior devices for absorbing impulsive pulses require two or three iron rings to be positioned between the worm gear 2 and the power output shaft 7. The rubber damper 5 is required to be cured to the iron rings. Therefore, the conventional arrangements are composed of many parts and manufactured in a number of complex processing steps, a fact which is not desirable for achieving a required degree of operation reliability of the devices.